Abstract：Plasma spectroscopy is an important detection object of the laser-induced breakdown spectroscopy technology. It mainly includes the characteristic spectra of sample atoms from highly excited state to low excited state through different paths. The identification of different characteristic spectra is an effective way to understand the characteristics of samples. The “Adjacent Principle” method is commonly used to identify the characteristic spectra in various commercial spectral measurement software. It was found that there were inevitable accidental coincidence errors during the identification of characteristic spectra by the “Adjacent Principle” method, resulting in a high error rate of spectral line identification.The mechanism of accidental coincidence error in the “Adjacent Principle” method was systemically analyzed. The wavelength difference between the characteristic peak of the laser-induced breakdown spectroscopy and the characteristic spectral line of the element directly affected the number of true coincidences. The experimental results showed that the true coincidence of the spectral line only existed in a certain wavelength difference range. Based on this characteristic,the self-calibration of wavelength drift of measuring spectra was realized. In addition, a weak accidental coincidence model was established to improve the accuracy of spectral line identification, and the automatic recognition of sample elements and spectral lines was realized. The weak accidental coincidence model overcame the shortcomings of the "Adjacent Principle" method, such as relying on experience to judge the distance between the experimental spectral line and the element characteristic spectral line, and relying only on a single characteristic spectral line to judge whether the element exists. In the weak accidental coincidence model, the threshold of coincidence number Tline, wavelength difference Twave and spectral peak seeking intensity Tpeak were added. The effects of thresholds Tline, Twave and Tpeak on the element recognition were analyzed, and the threshold was optimized so that the expected number of misidentified elements caused by accidental coincidence was less than 1, and the number of true coincidences of spectral line was maximized. By the weak coincidence model, the laser-induced breakdown spectra of standard sample FeNi alloy(GBW(E)010081),glass samples NIST610 and NIST612 were analyzed. The number of elements identified was 8,35 and 18, respectively, and the accuracy of element identification reached 100%. The analysis results showed that the identification rate of spectral lines with relative intensity of spectral characteristic peaks greater than 10% was higher than 60%.
[1] SPERANA M A,POMARES-ALFONSO M S,PEREIRA-FILHO E R.Analysis of Cuban nickeliferous minerals by laser-induced breakdown spectroscopy (LIBS):non-conventional sample preparation of powder samples[J].Analytical Methods,2018,10(5):533-540. [2] YANG Y,HAO X,REN L.Correction of self-absorption effect in calibration-free laser-induced breakdown spectroscopy(CF-LIBS) by considering plasma temperature and electron density[J].Optik,2020,208(12):163702. [3] HUDSIN S W,CRAPARO J,SARO R D,et al.Applications of laser-induced breakdown spectroscopy (LIBS) in molten metal processing[J].Metallurgical and Materials Transactions B,2017,48(5):2731-2742. [4] RZECKI K,SONICKI T,BARAN M,et al.Application of computational intelligence methods for the automated identification of paper-ink samples based on LIBS[J].Sensors,2018,18(11):3670. [5] KUMAR P,SOUMYASHREE S,RAO N,et al.Determination of stark shifts and widths using time resolved laser-induced breakdown spectroscopy (LIBS) measurements[J].Applied Spectroscopy,2020,74(8):913-920. [6] MA Yan,XIA Guo,HUANG Chan,et al.A simple and accurate wavelength calibration method for CCD-spectrometer[J].Infrared and Laser Engineering,2018,47(S1):S117002. [7] 檀兵,黄敏,朱启兵,等.激光诱导击穿光谱谱峰元素自动识别方法研究[J].中国激光,2018,45(8):273-279. TAN Bing,HUANG Min,ZHU Qibing,et al.Method on elements automatic identification of spectral peaks in laser-induced breakdown spectroscopy[J].Chinese Journal of Lasers,2018,45(8):273-279. [8] 吴少波,叶连慧. LIBS成分分析中元素谱线的自动识别方法[J].仪器仪表学报,2014,35(3):670-675. WU Shaobo,YE Lianhui.Automatic recognization method of element emission lines in composition analysis with LIBS[J].Chines Journal of Scientific Instrument,2014,35(3):670-675.
